Cleanup: Remove more forward declarations in various chrome/browser directories.

chrome/browser/plugin_prefs.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PLUGIN_PREFS_H_
 #define CHROME_BROWSER_PLUGIN_PREFS_H_
 #pragma once
 
 #include <map>
 #include <set>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "chrome/browser/prefs/pref_change_registrar.h"
 #include "content/public/browser/notification_observer.h"
 
 class Profile;
 
-namespace content {
-class ResourceContext;
-}
-
 namespace base {
-class DictionaryValue;
 class ListValue;
 }
 
 namespace webkit {
 struct WebPluginInfo;
 namespace npapi {
 class PluginGroup;
 class PluginList;
 }
 }
@@ skipping 125 matching lines @@
   // PluginList to use for testing. If this is NULL, defaults to the global
   // singleton.
   webkit::npapi::PluginList* plugin_list_;
 
   PrefChangeRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginPrefs);
 };
 
 #endif  // CHROME_BROWSER_PLUGIN_PREFS_H_